Asian rust and fungicides: Keeping the enemy at bay

You have to look hard, but there’s a silver lining on the rust-darkened cloud currently pouring gloom all over soybean country. If Asian soybean rust hadn’t been found so late this growing season, agriculture interests wouldn’t have the luxury of preparation — some four months’ worth — for the disease.

We’ve got time,” says Alan Blaine, Mississippi Extension soybean specialist. “That means the Section 18s can be dealt with, that means fungicides can be manufactured and shipped, that means everyone can be brought up to speed on how to scout for this.”

There may be time, but there’s little patience in the face of such a yield-sapping disease. (Yield losses of 80 percent have been reported in untreated fields in Zimbabwe.) In the early days following the rust’s confirmation, perhaps inevitably, concerns about fungicide supplies and availability have been voiced frequently.

“I have no reason to doubt that chemical companies will have the fungicide supplies we might need,” says Billy Moore, Mississippi Extension plant pathologist emeritus. “But I also know there are a lot of acres of soybeans in this country. If we find this rust next year, that’ll trigger spraying all over the place.

“There are no resistant varieties, so spraying would be a must. Hopefully, it can be held to one application, but most likely it’ll be two. That equals a lot of product, a lot of planes in the air, a whole lot of acres to cover. So it would be foolish not to admit we need to approach these issues promptly.”

Supply and demand

Keith Driggs doesn’t disagree and says his employer, Syngenta, is on the ball. The technical support representative says there’s a lot of bad information “floating around out there. The experience of South American producers … is that the strobilurin fungicide chemistries (including Quadris, Headline and Stratego) must be put out 100 percent preventive and aren’t often used alone.”

Instead, he said, mixtures of strobilurin and triazole chemistries (including Folicur and Tilt or Quilt, a premix of Quadris and Tilt which is not yet labeled in soybeans) works best.

Rick Chamblee, BASF technical services manager, said his company has found the same. “Triazole tank-mixed or in a pre-mix provides a knock-down, and the strobilurin enhances the residual.”

Headline is BASF’s leading fungicide, which contains the active ingredient F500. In South America, F500 in combination with a triazole is typically applied at early flowering (R-1), says Chamblee.

BASF expects Headline’s Section 3 to be approved by EPA in December. Following approval, the company will recommend Headline “be applied in conjunction with a triazole, most likely at R-1. However, growers should be scouting fields to see if rust shows up earlier.”

Bayer sells two materials — Folicur and Stratego — in South America. “Folicur, a preventive and curative, is the leading fungicide in terms of treated acres,” says a Bayer spokesman. “Stratego is primarily a preventive material.”

Triazole fungicides do have some curative action, says Chamblee. “The biggest problem with them in South America is they have limited residual power. This disease keeps rolling at you — it doesn’t give up.”

Thus the need for a residual in the tank-mix. Besides providing at least a few days of relief, such a brew will “stop the infection, if it’s already started,” said Chamblee. “(After application) producers need to continue monitoring fields and make a second application as needed.”

To stock up or not?

Manufacturing representatives say they’re fielding farmers’ questions on the need to stock up on fungicides now.

“Any run on fungicides is very premature,” says the Bayer spokesman. “Until we know what we’re dealing with, we discourage any inappropriate actions. It’s far too early for anything (like stockpiling) to be going on…. Taking a reasonable estimate of how we believe the disease will evolve, there’s no need to panic. (But whatever happens) we’re in a position to respond to the marketplace demands.”

“There’s a lot of fear that this will overwhelm us, fear it’ll cost producers $70 per acre to control, fear that there won’t be enough fungicide… all kinds of things,” says Driggs. “We don’t want to add to it — Syngenta wants no part in getting people to rush out and buy fungicides. We’re certainly going to make sure our supply isn’t pulled to one area or bought out.”

Based on models showing where the rust is expected to move, “we anticipate we — along with the entire industry — will have enough product available (to combat the rust),” said Tracy Linbo, marketing manager for BASF’s Headline.

“We’re also giving strict direction to our field people and customers not to stockpile product. These products are also used in key markets on high-value crops. We want to make sure there’s product available for all markets. Our competitors are doing the same — it’s an industry stance.”

Product Labels

BASF is in the “final stages” of receiving a Section 3 label on soybeans for Headline, says Chamblee. “We were looking for a Section 3 label before the soybean rust even appeared in the United States. So we’ll be using Headline in corn and soybeans even in areas where rust isn’t an issue.”

Bayer’s Folicur has already received Section 18 approval. Stratego is currently under review at EPA.

While producers are probably already familiar with Syngenta’s Tilt and Quadris, they may not know of a new fungicide, Quilt. Currently labeled for wheat and rice only, a number of states have requested a Section 18 exemption for Quilt on soybeans. For any state that gets the Section 18, “Quilt is our number one recommendation,” says Driggs.

In Arkansas — a state Driggs works along with southeast Missouri and west Tennessee — this season saw the most fungicide use ever. This is an advantage in dealing with the newly arrived rust because “fungicide use is already widely accepted. In Arkansas alone hundreds of thousands of acres have been treated with Quadris. That should prevent growers from having to absorb some of the newness and shock of using an unfamiliar product.”

Pulling the trigger

There are some absolutes when dealing with soybean rust. One is the fungal disease mustn’t be allowed to gain a substantial foothold in a field.

“The key to dealing with this disease is to be fully preventive or to catch it when it’s barely started,” says Driggs.

When to pull the spray trigger is a key decision farmers must make. And if someone wants to treat based on scouting alone, fine, says Driggs. But be forewarned, “That means a lot of hours spent in fields, hunting. This is not an easily identifiable disease in its early stages.”

Early on, the rust can be mistaken for “septoria or some of the other common soybean diseases,” says Linbo. “Everything we’ve seen from South America shows it’s more costly to growers if they’re playing catch-up instead of spraying preventively.”

If you’re going to scout, it’s very important to check in the canopy, says Chamblee. “You can’t ‘windshield scout’ with this disease. We believe the most difficult thing is making a timely application. If you start trying to play catch-up after seeing symptoms you may have lost yield already.”

Once a crop is more mature, the danger lessens. “Data from South America shows if the rust comes into a crop late — say R-5 to R-7 — it may make the crop ugly, but it won’t hurt the yields too much,” says Driggs. “But you’ve got to get the crop to that stage in good shape.”

Paying the price

Unable to say exactly how Asian soybean rust will affect next year’s crop (or if it will even show up), fungicide manufacturers are understandably skittish about making cost predictions. One thing they all agree on: the cost of several sprayings isn’t going to cost upwards of $50 as some reports have said.

“If it shows up, a producer may have to spray twice. That could cost around $30 or so,” says Driggs. “Any claims of sprayings costing $60 to $100 are absolutely ridiculous.”

“Based on what’s seen in South America,” says Chamblee, “we think our competitors are right in estimates of this costing $30 to $40 per acre.”

When a control program is managed properly, “I think the cost estimates should be on the conservative side,” says the Bayer spokesman. “Some people have built this up far more than it should be. We need to keep this in perspective.”

Some of the price predictions “are wild,” says Rick Cartwright, Arkansas Extension plant pathologist. Last year, over 1 million Arkansas soybean acres were sprayed with fungicides “at a cost of $15 to $20 per acre,” he says. “What those growers are probably looking at is an increase of $10 or $15. That’s not welcome, but it’s not $70 either.”

To lessen the sting of added input expense, Moore says in most cases of beans following beans, a fungicide application means “you’ll get a 5-bushel to 8-bushel yield response. In addition, such a spray will help control diseases other than rust. Those two factors will help with this extra input, at least a little.

“You know,” says Moore, “I keep thinking, ‘Even with rust they’re growing plenty of beans in South America. Plenty.’ And if they can do it, we can, too.”